1. Field of the Invention
The present invention relates to the exchanges of information between the ground and an aircraft by digital transmission. It relates more particularly to the selection of the most appropriate communications mode for establishing an air-ground and ground-air digital transmission link with an aircraft, taking account of the capabilities of the digital transmission networks existing on the ground in the area overflown by the aircraft, of the extent of the transmission facilities equipping the aircraft and of their availability as well as of the qualities and of the costs of the various communications modes possible at the instant in question.
2. Description of the Related Art
Exchanges of information in digital mode between an aircraft and the ground have the benefit of being more reliable than exchanges of phraseology in voice mode, since they do not depend on the intonation of the speaker and on the oral comprehension of a listener. It is for this reason that they are more and more being imposed in aeronautics, in supplement to or in replacement for voice-mode transmissions.
Thus an aeronautical digital communications network has existed since the 70""s, in Europe and in the United States, which is known by the title ACARS (an acronym for the expression in English: xe2x80x9cArinc Communication Addressing and Reporting Systemxe2x80x9d) and which has since been extended to near-global coverage. This ACARS aeronautical digital telecommunications network is implemented throughout the world on behalf of the airlines by various operators who offer ground-ground and ground-air coverage. It uses, at the choice of the pilot of the aircraft who makes the decision on the basis of the options of the moment, either a direct air-ground and ground-air digital communications mode by VHF sub-network according to a specific protocol, a mode known as: xe2x80x9cVDL Mode Axe2x80x9d (VDL being the abbreviation for the expression in English: Very High Frequency Data Link), or an indirect air-ground and ground-air digital communications mode by means of a sub-network of telecommunications satellites according to another specific protocol, a mode known as: xe2x80x9cSatcom Data 2xe2x80x9d, the protocols having been defined and standardized on the occasion of international conferences organized by the AEEC (an acronym for the expression in the English language: xe2x80x9cAirline Electronic Engineering Committeexe2x80x9d), which is a grouping bringing together airlines, aircraft manufacturers, equipment manufacturers and civil aviation authorities under the authority of ICAO (the International Civil Aviation Organization).
The ACARS aeronautical digital telecommunications network is very heavily used by aircraft (about 85% of the aircraft with more than 100 seats) to exchange messages with the airlines. Attempts have been made to use it in the same way for air traffic control, especially over the Pacific Ocean with the FANS-1/A ATC system (the acronym being an abbreviation of the expression in English: xe2x80x9cAir Traffic Control, Future Air Navigation Systems), but it exhibits characteristics which do not ensure security for air traffic control functions in areas of heavy traffic. This is because it allows only exchanges of printable characters, its reliability is limited to 94% and it is not encrypted and therefore unprotected against malevolent acts.
Aware of these difficulties, ICAO has had a new, higher-performance aeronautical digital telecommunications network defined and standardized, called ATN (abbreviation of the expression in English: xe2x80x9cAeronautical Telecommunication Networkxe2x80x9d), which is dedicated to information exchange between an aircraft and the ground for simultaneous activities of air traffic control, called ATC, and of information exchange with the airlines, called AOC (abbreviation of the expression in English: xe2x80x9cAeronautical Operational Communications). This ATN aeronautical digital telecommunications network, intended to be world-wide, can employ either an indirect air-ground and ground-air digital communications mode via a sub-network of telecommunications satellites at UHF according to a specific protocol known as: xe2x80x9cSatcom Data 3xe2x80x9d, or an air-ground and ground-air digital communications mode in line-of-sight mode, via a VHF sub-network according to another specific protocol, a mode known as xe2x80x9cVDL Mode 2xe2x80x9d, or an air-ground and ground-air digital communications mode, also line-of-sight but via a sub-network using a secondary radar according to yet another specific protocol, a mode known as: xe2x80x9cMode Sxe2x80x9d, or an air-ground and ground-air digital communications mode via an HF sub-network according to yet another specific protocol, a mode which is known as xe2x80x9cHF DLxe2x80x9d (an abbreviation of the expression in English: xe2x80x9cHigh Frequency Data Linkxe2x80x9d), and which uses the reflections in the upper atmosphere so as to get round the curvature of the earth and to obtain transmission links with a range greater than line of sight, the various protocols having been defined and standardized on the occasion of conferences organized by AEEC under the authority of ICAO. The choice between the various options for air-ground and ground-air digital communications modes of these sub-networks is made on the basis of the availabilities of the moment by an automatic unit known as xe2x80x9crouterxe2x80x9d, which acts without the knowledge of the pilot of the aircraft, on the basis of a standardized routing policy.
The larger capacity and the greater reliability of the ATN network mean that it is possible to transport, on an ATN network, messages available in the format of the ACARS network by means of an ACARS onto ATN gateway system installed at a software level on board the communications computers which are carried on the aircraft and which undertake the processing of the information to be exchanged, and within the ground terminal nodes of the ATN network.
The operational deployment of the ATN aeronautical digital telecommunications network is expected to take up to about the year 2015, at which time it should completely replace the ACARS aeronautical digital telecommunications network. Meanwhile the two networks will exist jointly, obliging the pilot of an aircraft who wishes to exchange information in digital form with the ground to choose the digital transmission method used: pure ACARS, ACARS onto ATN gateway or pure ATN, on the basis of his preferences, of those of his airline, of the transmission equipment of his aircraft and of the transmission equipment available on the ground in the area overflown, the choice of the ACARS or ATN network depending on the area of coverage.
Among the parameters influencing the pilot""s choice feature cost, performance and security of the communications, as well as the availability of the transmission equipment on board the aircraft and on the ground in the area overflown.
The cost of the communications is booked to the airline in the case of commercial information, or to the aviation authority (STNA in France, FAA in the USA, etc.), in the case of information relating to management of air traffic. It depends on the method of digital communications by sub-network employed for the exchanges with the ground (ATN satellite, ACARS satellite, ATN VHF radio, ACARS VHF radio, ATN HF radio, ACARS HF radio, mode-S radar transponder) and on the link on the ground between the radio-frequency receiving and sending head-end equipment and the terminal system targeted by the routers of the network.
The availability of the transmission equipment on board the aircraft depends on the physical communications facilities installed on board the aircraft, on their level of activity and on their capacity to establish a link in a given digital communications mode via a sub-network. These physical facilities consist of transmission-reception systems and of associated antennae. They are not necessarily all redundant for exchanges of information on the two aeronautical digital telecommunications networks, ATN and ACARS. It may be, for example, that the VHF and SATCOM systems are shared between the two networks, ATN and ACARS, and only usable alternately by one or other network. Neither are they all available at a given instant. For example, the pilot of an aircraft flying above an ocean far from the coasts has at his disposal only one communications mode, via a sub-network of satellites, whereas in other instances he may simultaneously use several communication modes via different sub-networks, for example a communications mode via a VHF sub-network and a communications mode via a sub-network of satellites, or even two communications modes via a VHF sub-network, one according to an ACARS protocol, the other according to an ATN protocol.
In the case which is most widespread nowadays, of an aircraft equipped to support only the ACARS aeronautical digital telecommunications network, there is a computer on board which is specialized in the management of communications according to the ACARS protocols. This computer is accessible to the pilot via a man-machine interface called: MCDU (abbreviation for the expression in English: xe2x80x9cMultifunction Control and Display Unitxe2x80x9d), which allows the pilot to choose between three possible operating modes: the first only allowing information exchange in digital mode according to the communications mode by VHF sub-network only, called VDL mode A, the second only according to the communications mode via a satellite sub-network called Satcom data 2, and the third either according to the communications mode via a satellite sub-network called Satcom data 2 if it is available, or, by default, according to the communications mode via a VHF sub-network called VDL mode A.
In the future, for an aircraft equipped to support the two aeronautical digital telecommunications networks ACARS and ATN, there will be one or more computers on board specialized in the management of the communications either according to the protocols of the ACARS network, or according to the protocols of the ATN network, and the pilot will have to choose the network used by means of an MCDU man-machine interface. This configuration is not optimal since it implies an additional workload for the pilot of the aircraft, who has to take care to make the correct choice of telecommunications network all along the path travelled by the aircraft. Moreover, it does not make it possible to take advantage of all the options of the two aeronautical digital transmission networks ACARS and ATN which the transmission equipment on board the aircraft and on the ground might allow. This is because, in the case of the use of the ATN network, it has to have priority of access to the on-board transmission-reception systems by reason of the security constraints imposed for the transmission of information involving air traffic control. However, there may be on-board transmission-reception systems left free or partially used by the current routing of the ATN network, either because they do not contribute to the physical link or links chosen by the routing of the ATN network, or because there is dead time between the periods of information exchange on the ATN network. When they are not engaged by the ATN network, these transmission-reception systems may be put to use to add, to a digital transmission via the ATN network, an ancillary digital transmission via the ACARS network.
The object of the present invention is to relieve the pilot of an aircraft which is equipped to support the aeronautical digital telecommunications networks ACARS and ATN of the workload of the tasks for selecting the appropriate aeronautical digital telecommunications network or networks on the basis of the capabilities of the area on the ground overflown by his aircraft, as well as to offer this pilot an automated choice of an optimal configuration of one or more communications modes via a sub-network to be allocated to the information exchanges in digital mode, this choice taking account, in addition to the capabilities of the area on the ground overflown by the aircraft, of the level of activity of the transmission equipment of the aircraft, of the transmission costs, of the performance and of the reliability of the communications modes via a sub-network which are available at every instant, of any directives from the pilot and more generally of the quality of service demanded.
The subject of the invention is a method of managing communications modes for the exchange, in digital form, of messages between the ground and an aircraft which is provided with transmission equipment suitable for the aeronautical digital tele-communications networks ACARS and ATN and for their various transmission sub-networks, and which is equipped with a computer undertaking management of the communications of the aircraft within an ACARS or ATN network, and with a man-machine interface allowing its pilot to have a dialogue with the said computer. This method consists:
in providing the said computer with a database holding, at every instant:
the updated status of the communications modes via a sub-network of the two networks ACARS and ATN recorded as being available for the aircraft at the desired moment of the exchange, taking account both of the capabilities of the transmission equipment of the ground area overflown by the aircraft and of those of the transmission equipment of the aircraft,
the directives framing the choice of configuration which are expressed by the pilot by way of the man-machine interface,
a pre-established routing policy, and
the costs, the performance levels and qualities of service of the various communications modes via a sub-network which are offered by the two transmission networks ACARS and ATN, and
in programming the said computer so as automatically to select a mode of communication via a sub-network of the ACARS or ATN transmission networks for an exchange, in digital form, of information between the aircraft and the ground, by application of a predefined rule of choice taking account of an order of preference among the various communications modes via a sub-network of the ACARS and ATN transmission networks which is established on the basis of the elements of the database: actual availabilities, at the desired moment of the exchange, of the communications modes via a sub-network for the two ACARS and ATN transmission networks, directives expressed by the pilot framing the choice of the communications mode via a sub-network to be used, pre-established routing policy, costs, performance levels and qualities of service of the various communications modes via a sub-network which are offered by the ACARS and ATN transmission networks.
Advantageously, the selection of a communications mode via a sub-network of the ACARS and ATN networks to be used for the exchange of AOC as well as ATC applications messages is made by application of a reliability criterion consisting in allocating, to the communications modes via a sub-network belonging to the ATN network, a better reliability preference mark than to the communications modes via a sub-network belonging to the ACARS network, so that the more reliable network, that is to say the ATN network, is chosen by default, the ACARS network being chosen only outside the coverage of the ATN network.
Advantageously, the selection of a communications mode via a sub-network of the ACARS and ATN networks to be used for the exchange of messages is made by application of a cost criterion consisting:
in allocating to the various communications modes via a sub-network a preference mark which is higher in inverse proportion to the overall end-to-end communications cost,
in determining whether a communications mode via a sub-network belonging to the ATN network is already active at the desired moment of the exchange of messages and in consulting its cost-preference mark,
in determining the communications modes via a sub-network belonging to the ACARS network, which are available at the desired moment of the exchange of messages, on the basis of the transmission equipment of the aircraft which is not used by the ATN network at that moment, and in consulting their cost-preference marks,
in selecting, from among the communications modes via a sub-network which were previously adopted, the communications mode via a sub-network having the best cost-preference mark, and
in recommencing the preceding operations upon each alteration to the database resulting either from the appearance of a new available communications mode via a sub-network, or from the loss of availability of a communications mode via a sub-network resulting from the movement of the aircraft or from an alteration of its flight conditions, or from a switch-over of the routing of the ATN network when the latter is active.
Advantageously, the selection of a communications mode via a sub-network of the ACARS and ATN networks for the exchange of messages is made by allocating to the various possible communications modes via a sub-network of the ATN and ACARS networks a preference mark decreasing as a function of an order of priority established on the basis of the pre-established routing policy and by selection of the communications mode via a sub-network having the highest preference mark among the communications modes via a sub-network which are available at the desired moment of the exchange of messages, taking account of the area of the ground overflown by the aircraft, of the pilot""s preferences and of the availability of the transmission equipment of the aircraft.
The implementation of such a method of managing communications modes between the ground and an aircraft provided with transmission equipment suitable for the aeronautical digital telecommunications networks ACARS and ATN makes it possible to have communications via the ATN and ACARS networks existing side by side, with no additional workload for the pilot of the aircraft, by automatically choosing the configuration which is most suitable, from the point of view of the reliability, the cost or the preferences expressed by the pilot or his airline, for exchanging information with the ground, without in any way excluding a manual choice. It also makes it possible to manage conflicts of use by the ACARS and ATN networks of the on-board transmission equipment of the aircraft and thus makes it possible to have certain on-board transmission equipment of the aircraft used in common by the ACARS and ATN networks, by time-sharing, which makes it possible to reduce the amount of transmission equipment installed on board the aircraft.